1. Field of the Invention
This invention relates to a gum removing solution facilitating the removal of a gum material which is applied to a lithographic plate for protecting the non-image part thereof.
2. Description of the Prior Art
Lithography is a printing system where the hydrophilic property of the image area of a printing plate is utilized, and, after development, a process has generally been practiced in lithography in which a developing ink is applied to the image areas and a gum solution is applied to the non-image areas, for the purpose of maintaining and reinforcing the properties of both of these areas. The gum solution comprises an aqueous solution of gum arabic, cellulose gum or a water-soluble high molecular weight substance containing carboyl groups in the molecule, and optionally contains a pH adjusting agent and/or an antiseptic. The object of the gum solution is not only to protect the hydrophilic property of the non-image areas but also to protect the areas from stains and scratches resulting from a retouching of the other image areas such as when changes or erasures are made, or from adhesion of fingerprints, fats and oils and dust thereto occurring during storage of the printing plates between producton and uses for printing, or storage for re-use or during installation on a printing machine, or, that is, to prevent the occurrence of any oxidative stains. oxidative stains are those phenomona which occur, when the printing plate is made of a metal plate such as an aluminum or zinc plate, and the surface of the metal plate is oxidized after the surface has been exposed continuously for a long period of time during manufacture of the plate or during printing with the plate, causing the occurrence of spotted ink stains on the surface, and these stains can be prevented by provision of a gum coating on the surface of the printing plate.
The gum coating is preferably easily removed on a printing machine, and in particular, this is desirably completely removed in a short period of time. The reason for this is the organophilic property (or ink receptivity) of the image area is extremely degraded, if the gum coating remains in an image area during printing.
Recently, a process has been developed where the conventional step for application of a developing ink to an image area is omitted to reduce the late making steps or to save labor. In such a process, however, the gum tends to adhere to the image area, and the gum adhered to the image area is often difficult to remove. As one labor-saving means, a process has been devised where the protection of both the oleophilic property of the image area and the hydrophilic property of the non-image area is simultaneously carried out in one step. The gum solution used in this process in general contains an emulsified oleophilic material therein. When such a gum solution is actually used, however, the gum adhering to an image area is more difficult to remove than the gum contained in an aqueous soluton of gum arabic only.